Over the past 4 years considerable data has argued that insulin increases skeletal muscle blood flow in healthy humans and insulin resistance in NIDDM and obese skeletal muscle is accompanied by a diminished vascular response. It is not known whether the increase in muscle blood flow is due to enhanced flow to previously perfused muscle or to recruitment of new capillary beds. Using two techniques developed in our laboratories we will test the hypothesis that insulin and I GF-I act to open new capillary beds.